Hydraulic control system



sept- 6 1955 J. A. HARDY HYDRAULIC CONTROL SYSTEM 2 Sheets-Shee l Filed Oct* 14, 1952 H rml Sept. 6 1955 1. A. HARDY 2,716,946

HYDRAULIC CONTROL SYSTEM Filed Oct. 14, 1952 2 Sheets-Shee 2 ci) b3 70 INVENTOR.

:f7/V55* /Z #fria/f United States Patent O HYDRAULIC CONTROL SYSTEM James A. Hardy, Indianapolis, Ind., assignor to Schwitzer- Cummins Company, Indianapolis, Ind., a corporation Application October 14, 1952, Serial No. 314,682

Claims. (Cl. 10337) This invention relates to a hydraulic steering system, particularly for a heavy duty vehicle control, in association with a source of fluid pressure of a nature developed by a variable displacement pump.

In hydraulic steering systems involving uid power actuation through finger tip control, the steering wheel or the like is manually operated to bring into play hydraulic power which then takes over and provides the operating force for the steering mechanism. When the vehicle is driven in a straight or nearly straight path, only a very small amount of hydraulic Huid is required, but when it is desired to make a turn, and particularly a quick turn, it is desirable to bring into play a substantial amount of hydraulic iluid under rapid flow and high pressure. k

It is therefore the object of this invention to provide a pressure and flow control, as well as a temperature control which will automatically deliver the proper iluid pressure and flow to the steering mechanism, depending upon the extent to which it is to be deviated from the normal or straight line.

For accomplishing the invention there is provided the usual variable displacement pump connected with a source of hydraulic fluid, such as oil, which pump is provided, in addition to its intake, with dual discharge outlets, one for a rapid flow or high G. P. M. and the other for delivering a relatively low ow or-low G. P. M.

The above contemplates the association with the ilow and pressure control, of a thermostatic control such as to neutralize the pump upon the hydraulic iluid rising to an excessive or high predetermined temperature.

The full nature of the invention will be vunderstood from the accompanying drawings and the following description and claims:

Fig. l is a central vertical section through a variable displacement pump, the ow control valve and fluid displacement control cylinder schematically illustrating the invention.

Fig. 2 is a section taken on the line 2--2 of Fig. 1.

Fig. 3 is an enlarged sectionaliview of a portion of the mechanism shown in` Fig. 1.

Fig. 4 is an enlarged sectional view of a portion of the mechanism shown in Fig. 2.

In the drawings there is schematically illustrated a hydraulic control system particularly adaptable for vehicle steering, including a variable displacement vane type pump having a housing 10. Within the housing there is provided a driving shaft 11 to which there is keyed a rotor 12, said shaft being driven from any suitable source of power. Radially slidable through the rotor 12 there is a plurality of vanes 13, all operating within a fluid displacement varying member herein shown as the pumping ring 14 surrounding and spaced from said rotor. Within the rotor there is a pair of retaining rings 15 such as to hold the vanes in contact with the inner ,surface` of the pumping ring. Said pumping ring is pivotally mounted on a pivotpin 16 for permitting it to swing from a non-pumping concentric position relative to the 2,716,946 Patented Sept. 6,1955

rotor to a pumping eccentricposition, as shown in Fig. 1.

Thus, the variation in eccentricity of the pumping ring relative to the rotor varies the tiuid displacement of the pump and therefore varies the rate of flow of the hydraulic uid, such as oil.

A discharge port .17 is positioned so thatthe center of the area which is `subjected to high pressure on the underside of the pumping ring is to the left of its pivot point, 4as shown in Fig. l. Pressure on this area produces torque about the pumping ring which urges the pumping ring or fluid displacement varying member toward its non-pumping position. Opposite the discharge port 17 there is an intake port-18 communicating with an internal chamber 19 of the pump housing. Communicating with the internal chamber there is an intake line 20 leading from a hydraulic uid tank 21.v

The discharge port 17 communicates with a discharge outlet passage 22 which has its principal or high rate of ow line 23 connected therewith. For example, the system as herein illustrated is designed to produce a high tlow rate through the line 23 in the order of 70 G. P. M. Beyond the line 23 the passage 22 communicates with a low rate tlow line 24 which, for example, carries a ow rate in the order of l0 G. P. M. Said ilow rates are controlled through a ow control valve 25 interposed between the passage 22 and the line 24 (Fig. 3).

The flow control valve comprises a reciprocating piston Valve 26 slidably mounted in a cylinder 27 formed in the housing. The piston in said valve is provided with a central bore 28 and is normally positioned in the cylinder under the force of a spring 29 which is adjusted to maintain the desired flow rate such as in the order of 10 G. P. M. The piston is provided with an annular recess 30 which registers with a port 31. The port 31 communicates with a passage 32. The piston is also provided with a second annular recess 33 adapted to bridge the ports 34 and upon retraction of the piston against the force of the spring 29. There is at the near end of the piston a plurality of small ports 36 leading from the front face thereof in communication with the passage 22, to the recess 30. The port 34 communicates with the passage 32 andthe port v35 communicates with the passage 37. Thus, during normal operation the iluid will be pumped into the line 23 and into the line 24 through the bore 28 of the flow control valve, a limited ilow passing through the ports 36 to passage 32. The passage 32, as well as passage 37, leads to a maximum pressure relief valve 38 operating in conjunction with and controlling a fluid displacement control cylinder 39 operatively connected with the pumping ring 14 for controlling the eccentricity of the pumping ring and the rate of Huid displacement.

' The relief valve 38 includes a reciprocating piston 40 having abore 41 communicating with the control cylinder 39 and an annular recess 42. Thus, in normal position fluid may ow from the discharge outlet 22 through the ports 36 and passage 32 into the control cylinder 39. The piston is backed up and retained in its normal position, as shown in Fig. 3, by a compression spring 43 set for a maximum pressure which may be of the order of 1000 p. s. i. Reciprocating in the control cylinder 39 there is a piston 44 connected by a piston rod 45 with an arm 46 extending somewhat tangentially downwardly from the pumping ring 14.

Connected with the lines 23 and 24 leading from the pumpthere is provided a manually actuated iiuid control valve 47 which includes a cylinder 48 in which there is slidably mounted a sleeve 49. One end of the sleeve is connected to an actuating rod 50 which in turn is connected to the steering gear of the vehicle. Upon the steering gear being turned from one direction to another, the rod 50 will be reciprocated. When the steering operation is in a straight line with no deviation, thesaid rod and sleeve will be in neutral position. It is yieldingly retained in neutral position by a compression spring 51, but which spring permits the sleeve to be slidably moved in either direction vwithin the cylinder, 'depending upon thedirection in which the vehicle is to be turned.

vThe cylinder is formed with a by-pass 52 communicating with two annular recesses 53 and 54,' and with one end thereof communicating with an annular recess 55 formed about the periphery of the sleeve. Said sleeve is also provided with a series of peripherally spaced ports 56 and 57 and also an annular recess 58. At the opposite end of the control valve from the steering rod 50, its cylinder is connected through a discharge line 59leading to the source of hydraulic uid or tank 21.

Connected with the uid control valve 47 there yis an actuating cylinder 60 in Which there is mounted a reciprocating piston 61 connected by a piston rod 62 to the steering mechanism of the vehicle, said piston operating centrally of the cylinder to leave a chamber 63 on one side thereof and a chamber 64 on the other side. The chamber 63 is connected with a iluid line 65 and the chamber 64 with a fluid line 66.- When the piston 61 is in the position shown, the steeringgear and mechanism are in neutral position or set for straight line travel. When the steering gear is operated in one direction, tluid will be forced through the line 65 into the chamber 63 to exert hydraulic pressure on the piston 61 for driving the mechanism in the corresponding direction. When the -steering gear is reversed, hydraulic fluid will be forced through the line 66 into the chamber 64 for moving the piston in the opposite direction to reverse the steering mechanism. The fluid control valve 47 is such that upon uid being forced through one line 65, 66, it will be relieved and returned through the other line.

In the neutral or direct line travel position, the high tiow line 23 will be blocked off by control valve`47 since very little uid is required, ample ow being permitted through the low flow line 24 into the recess 55 of the sleeve. Upon the sleeve being caused to move slightly by slight turning of the steering Wheel in maintaining a straight line travel, one way or the other, it will barely uncover one or the other line 65 or 66. In fact, with the t sleeve in absolute neutral position there will be some leakage to or from lines 65, 66 respectively due to the convex surface of the sleeve intermediate recesses 55, 56 and 57. Therefore, during such straight line travel with only slight movement of the steering wheel and the sleeve 49, oil flow on the order of l G. P. M. will seep through recess 55 alternately into lines 65, 66 and relievedthrough recesses 56, 57 respectively. This is ample for maintaining the desired diierential tluid pressures in the chambers 63 and 64, it being undesirable to introduce a high rate of ow thereto under such conditions.

very rapid and instantaneously high flow of uid to fill the one chamber 63, 64, and relieve thel other. When thatoccurs the steeringwheel moves the sleeve 49 in one or the other direction sufliciently to cause the recess 58 in the sleeve to uncover or'bridge the line 23- and either of the recesses 53, 54.

Thereupon, the high rate vof ow, such as in the order of 70 G. P. M., will flow from Vthe line 23 into theby-pass 52 and join with the line 24 to provide an aggregate flow, such as in the order of 8O G. P. M., into the recess 55 of the sleeve which will in turn register completely with one or the other lines 65, 66. At the same-time, the other line will permit rapid return flow of the fluid through one of the ports 56, 57, into the sleeve for discharge through the line 59 back to the source 21.

lt will therefore be observed that through the medium of theuid control valve 47 and the high and lowfow connections 23, 24 therewith, the hydraulic steering mechanism will be provided with ample flow of fluid for rapid and instantaneous movement underl full pressure when However, when 4 the wheel 1s given a sudden turn, it is necessary to-have a Vrequired, while it will not be necessary for the pump to produce such high rate of flow when not required. For example, the pump herein 'shown may be designed to have a maximum capacity of 80 G. P. M. at 1200 R. P. M. against 1000 p. s. i. pressure. At high speeds the maximum flow will not exceed the predetermined maximum G. P. M. At speeds below 1200 R. P. M. the maximum ow will be less than such predetermined maximum 80 G. P. M.

From the above description it may be observed that the automatic controls will provide only the required amount of uid for steering. The pump will not pump excess fluid throughl the system or'produce more pressure than is required. The horsepower required to drive the pump will be kept at a minimum. This not only saves power but also reduces heat in the hydraulic system. When the vehicle is being driven in a nearly straight line, large amounts of fluid or high flow thereof are not required. Under these conditions the sleeve 49-of the fluid control valve will not normally be moved far enough to uncover either of the recesses 53, 54 for permitting high flow from the line 23. When these recesses are closed by the valve sleeve no `oil can ow from the discharge line 23 of the pump, but must pass through the flow control valve 25 and the low flow line 24.A

Referring again to the ow control valve 25,'it is to be understood that the spring 29 is adjusted so that the rate of flow through the bore 28 will produce suiiicient pressure drop across the valve to move it against the force of the spring, it being noted that there will be a differential pressure on the ends of the piston 26, depending upon the rate of ow therethrough. If the rate of ilow is less than that for which the springis set, -such as on the order of l0 G. P. M., the piston 26 of the valve will be in the position shown in Figs. 1 and 3. VWith the piston in this position uid will ow through the small ports 36 and port Tal-through passage 32 and bore 41 into the uid displacement control cylinder 39. The uid entering this cylinder will exert lsuch pressure on the piston 44 as to tend to move the pumping ring 14 toward its eccentric position increasing the rate of displacement, whereupon the rate of ow from the pump will increase until the maximum ow for which the spring 29 is set (l0 G. P. M.) is obtained. If the ilow exceeds this rate, the piston 26 willbe moved to the left, cornpressing spring 29 and closing port 31.

Y `Thereupon the passages 34, 35 will bebridged by the recess 33 in the piston. The fluid is thereby permitted to ow `from the control cylinder 39 back through the passage 32', ports 34 and 35 and out through a lpassage 37a into the intake chamber 19 of the pump. `Such release of the uid from thecyliuder 39 will permit the pumping ring to move toward its concentric non-pumping position, thereby reducing the ow' to maintain it at the predetermined rate.

However; upon rapid' movement ofthe steering gear, the sleeve 49 in the duid-control valve will open upthe high ow line 23. Opening the line 23 permits a high ow of-oil-to join with the oil from line 22 and provides the necessary capacity for fastV steering. Anorice 75vis installed in line 23 so that when 70 G. P. M.l=is"flowing through line 23a'nd10'G. P. is owing through li'n'e 22, theV pressure drop across the ow controlvalve 2S will again begreat enough to move its 'pistonf26 for limiting the total How to G. P. M.

The maximum pressure developed by the pump is limited by the relief valve 40. This valve' is' installed atthe end of the uid displacement control "cylinder 39. 'Pressure in' the pumping ring produces at'orque about 'the' pivot pin which tends to reduce the eccentricity. The 'torque will produce a force on the eccentricity' control piston 44. The force on piston 44 produces a pressure in 'cylinder 39. This pressure acts on the end -of "relief"valve piston 4G. When the pump pressure reaches' asuicientlyliigh value (on the order of 1000 p. s. i.) the pressurel on the end of piston 40 will move it to theleft against the force of spring 43. Such movement of the piston will close the inlet pasage 32 from the flow control valve and connect the bore 41 leading from the cylinder 39 with the passage 37a. The fluid will thereupon escape from the cylinder, permitting the piston 44 to move to the left and the pumping ring to move toward its concentric non-pumping position. Thus, the pressure is limited, irrespective of delivery of fluid, in accordance with the force of spring 43.

For reducing the fluid displacement of the pump in event excessive temperature is developed, there is provided a thermostatic control valve, as shown in Figs. 2 and 4. For this purpose, the housing is provided with a chamber 67 in which there is mounted a thermostatic element 68, which upon expansion engages and displaces a piston valve 69 operating in a cylinder 70 against the force of a spring 71. Said element is so positioned that upon the fluid in the chamber 67 rising in temperature, the piston 69 will be displaced sufliciently to cause a recess 72 therein to bridge and interconnect the passages 73, 74 formed in the housing, and wherein the passage 73 has one end communicating with the intake side of the pump housing at 19 and with the chamber 67 and the interior of the cylinder 70. The passage 74 communicates with the fluid displacement control cylinder 39.

If the oil becomes excessively heated, the thermostatic unit will force the piston 69 to the right against the force of the spring 71, whereupon oil will be released from the cylinder 39 and thereby permit the pumping ring to move toward its non-pumping position so that less fluid will be pumped thereby until the temperature is reduced sufficiently to close the passage 74 and sufficient pressure built up in the cylinder 39 to cause the pumping action to resume.

From the above description it may be seen that the automatic controls will provide only the amount of hydraulic fluid required for the steering operation, and no more. rl`he pump will not displace excess fluid through the system or produce more pressure than is required. The driving power and heat generated will thereby be maintained at a minimum.

The invention claimed is:

l. In a hydraulic control system, the combination with a variable displacement pump having a fluid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a fluid displacement control cylinder and piston connected with said pump member, a fluid pressure passage leading from said outlet to said cylinder, a relief passage leading from said cylinder, a flow control valve interposed in said pressure passage comprising a valve piston having a passage leading from said outlet to a service line, and a spring urging said piston in a direction to open said pressure passage, said piston passage and spring being proportioned to position said valve piston to open said pressure passage up to a predetermined flow through said piston passage and cause said piston to close said pressure passage and open said relief passage upon a greater flow through said piston passage.

2. In a hydraulic control system, the combination with a variable displacement pump having a fluid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a fluid displacement control cylinder communicating with said outlet, a piston operable in said cylinder connected with said pump member, a fluid pressure passage leading from said outlet chamber to said cylinder, a relief passage leading from said cylinder, a piston valve interposed between said passages, and a spring positioned to bias said piston valve to open said pressure passage and close said relief passage, said spring being tensioned to permit said piston valve to move into position to close said pressure passage and open said relief passage upon greater than a predetermined maximum fluid pressure being developed in said outlet.

3. In a hydraulic control system, the combination with a variable displacement pump having a fluid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a fluid displacement control cylinder communicating with said outlet, a piston operable in said cylinder connected with said pump member, a fluid pressure passage leading from said outletto said cylinder, a relief passage leadingfrom said cylinder, a piston kvalve interposed between said passages, a spring positioned to bias said piston valve to open said pressure passage and close said relief passage, said spring being tensioned to permit said piston valve to move into position to close said pressure passage and open said relief passage upon greater than a predetermined maximum fluid pressure being developed in said outlet, anda flow control valve interposed in said pressure passage biased to maintain said passage open up to a predetermined rate of flow and close said passage and relieve said cylinder upon a greater rate of flow.

4, In a hydraulic control system, the combination with a variable displacement pump having a fluid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a fluid displacement control cylinder communicating with said outlet, a piston operable in said cylinder connected with said pumping ring, a fluid pressure passage leading from said outlet to said cylinder, a relief passage leading from said cylinder, a piston valve interposed between said passages, a spring positioned to bias said piston valve to open said pressure passage and close said relief passage, said spring-beingy valve interposed in said pressure passage comprising a piston valve having an axial bore leading from said' outlet to a service line, and a spring urging said last mentioned piston valve in a direction to open said pressure passage, said bore and spring being proportioned to position said last mentioned valve to open said pressure passage up to a predetermined flow through said bore and cause said last mentioned valve to close said pressure passage and open said relief passage upon a greater flow through said bore.

5. In a hydraulic control system, the combination with a variable displacement pump having a fluid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a fluid displacement control cylinder communicating with said outlet, a piston operable in said cylinder connected with said pump member, a relief valve associated with said cylinder biased to cylinder closing position and movable under predetermined fluid pressure in said cylinder to cylinder opening position for relieving the fluid pressure therein and permitting said pump member to move toward its non-pumping position, a thermostatic element associated with the interior of the pump, a valve actuated by said element, and fluid passages leading from said control cylinder to the intake side of said pump through said valve, said valve being positioned by said thermostatic element to close said passages at normal operating temperature and open said passages to relieve said cylinder at an excessive temperature.

6. In a hydraulic control system, the combination with a variable displacement pump having a fluid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a fluid displacement control cylinder and piston connected with said pump member, a fluid pressure passage leading from said outlet to said v 1 cylinder, a ow control valve interposed in said pressure passage biased to maintain said passage open up to a predetermined rate of flow and close said passage and relieve said cylinder upon a greater rate of ow, a thermostatic element associated with the interior of the pump,V a valve actuated by said element, and uid passage leading from said control cylinder to the intake of said pump through said last mentioned valve, said valve being positioned by said thermostatic element to close said passage at normal operating temperature and open said passage to relieve said cylinder at an excessive temperature.

7. In a hydraulic control system, the combination with a variable displacement pump having a uid inlet and discharge outlet, and a fluid displacement varying memberV urged toward its non-pumping position by the fluid presv sure in said outlet, of a high rate of ow line, a low rate of'ow line, said lines being connected with said outlet, a manually actuated uid control valve to selectively connect said flow lines with the work, a fluid displacement control cylinder communicating with said low flow line,

a piston operable in said cylinder connected with said pump member, and a relief valve associatedwith said cylinder biased to cylinder closing position and movable under predetermined uid pressure in said outlet to cylinder opening position for relieving the fluid pressure therein and permitting said pump member to move toward its non-pumping position.

8. In a hydraulic control system, the combination with a variable displacement pump having a uid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a high rate of ow line, a low rate of ow line, said lines being connected with said outlet, a manually actuated uid control valve to selectively connect said ow lines with the Work, a fluid displacement control cylinder and piston connected with said pump member, said cylinder .being connected With said low iiow line, and a flow control valve interposed in said low ow line intermediate said cylinder and outlet biased t to maintain said line open up to a predetermined rate of flow and close said line and relieve said cylinder upon a greater rate of ow.

9. In a hydraulic control system, the combination with a variable displacement pump having a fluid inlet and discharge outlet, and a fluid displacement varying member urged toward its non-pumping position bythe uid pressure in said outlet, of a high rate of ow line, a low rate of flow line, said lines being connected with said outlet, a` manually actuated fluid control valve to'se- U lectively connect said .flow lines with the Work, a fluid displacementicylinder and pistonl connected with said pump member, `said cylinder being connected with said low ow line, a relief passage leading from said cylinder, a How control valve interposed inA said pressure passage comprising avalver piston having an axial bore Vleading from said outlet to said low flow line, and a spring urging said piston in a direction to open said pressure passage, said bore and spring being proportioned to position said valve piston to open said pressure passage up to a predetermined flow through said-bore and cause said piston to close said pressure passage and open said relief passage upon a greater iiow through said bore.

i0. ina hydraulic control system, the combination with a variable displacement pump having a fluid inlet i and discharge outlet, and a uid displacement varying member urged toward its non-pumping position by the fluid pressure in said outlet, of a high rate of flow line, a low rate of oW line, said lines being connected with said outlet, amanually actuated fluid control valve to selectively connect'said ow lines with the work, a fluid displacement control cylinder and piston connected with said pump member, said cylinder being connected with said low ow line, a relief passage leading from said cylinder, a ow control valve interposed in said pressure passage comprising a valve piston having an axial bore leading from said outlet chamber to said low flow line, a spring urging said piston in a direction to open said pressure passage, said bore and spring being proportioned to position lsaid valve piston to open said pressure passage up-to a predetermined flow through said bore and cause said piston to close said pressure passage and open said relief passage upon a greater How through said bore, a thermostatic element associated with the interior of the pump, a valve .actuated by said element, and a uid passage leading from said control cylinder to the intake side of said pump through said valve, said valve being positioned by sa'id element to close said passage at normal operating temperature and open said passage to relieve said cylinder at an excessive temperature.

.- References Cited in the le of kthis patent UNTED STATES PATENTS 2,080,810 Douglas May 18, 1937 2,142,275 Lane Ian. 3, i939 2,166,423 Clark July 18, 1939 2,600,632 French June 17, 1952 2,600,633 French June 17, 1952 2,606,503 Shaw Aug. l2, 1952 

